This invention relates to electromagnetic actuators. More particularly, it relates to improving the efficiency of such actuators.
Linear actuators have been known in the art for many years. One type that has been used in a wide variety of applications is the so-called voice coil or moving coil motor. In motors of this type, when a current is applied to a coil positioned in a magnetic field with a segment of the coil perpendicular to the field, a force is exerted on the coil segment. The direction of this force is dependent upon the direction of current flow and the direction of the magnetic field. For a magnetic field of given density, the force produced is directly proportional to the applied current. Because of this proportionality, moving coil linear actuators have been widely used as electromechanical transducers. Also, such motors have been used to precisely control the position of an output member. In the computer industry, for instance, they precisely move magnetic heads that read or write data on rotating data storage discs. In the photographic field, these motors have been useful for effecting actuation of shutter blades. There exists a wide variety of motor constructions for driving shutter blades. U.S. Pat. No. 4,227,100 discloses an electromagnetic linear actuator having two movable and independently actuatable coils energized by a single magnetic circuit. U.S. Pat. No. 4,306,793 discloses an electromagnetic actuator usable for driving a pair of shutter blade assemblies.
With motors of the above type, it is important that they are as efficient as possible and that their output response be uniform. Towards this end, it is desirable to control the lines of flux so that they travel through the working gap and coil in one direction with respect to the coil windings.
One common approach is to place a magnetic field reinforcing member, for instance, a steel plate, above the coil windings so that magnetic lines of flux emanating from a magnetic field below the windings travel completely through the coil windings. Another approach for controlling flux is disclosed in U.S. Pat. No. 4,306,788. However, this patent discloses a relatively complicated actuator having a plurality of magnetic circuits wherein only a single coil can operate a shutter arrangement. Examples of other known approaches for improving the efficiency of a motor by controlling the lines of flux are shown in U.S. Pat. Nos. 2,833,968 and 3,723,780.